The present invention relates to wireless communication applications, more particularly to modem alignment in wireless communication systems.
Explosive growth in the market for internet and intranet related applications has provided the impetus for a greater demand for fixed wireless networking services and systems. A wireless internet access system (WIAS) illustrated in FIG. 1 is composed of four major parts: (a) multiple data base stations (BS) 100(a) and 100(b) which provide wireless connectivity and radio coverage to subscriber units 102(a)-(d) (for example, residential and corporate terminal equipment as illustrated in FIG. 1) of a large geographical area; (b) wireless modems 170(a)-(c) (hereinafter xe2x80x9cWMxe2x80x9d) which are connected to BS 100(a) or 100(b) via wireless links 115(a)-(c); (c) a data switching center (DSC) 125 with integrated management functions; and (d) a backbone transmission network 135 interconnecting (a)-(c) above.
As can be seen from FIG. 1, corporate terminals 102(c) and 102(d) can be, and many times are, connected to WM 170(c) via a local area network (LAN) and a wireless router or firewall (not shown). Additionally, BS 100(a) and 100(b) may communicate with DSC 125 via frame relays (not shown). Further in conventional wireless internet access systems or networks, DSC 125 is interconnected with backbone transmission network 135 by a router and/or firewall (not shown for clarity).
FIG. 2 illustrates BS 100(a) and 100(b) of FIG. 1 in an operational mode. Each BS 100(a) and 100(b) provides 360xc2x0 RF coverage on the order of several gigahertz (preferably operating in the 3.5 GHz spectrum using approximately 5 MHz wide channels), sending and receiving signals over air links 115(a)-(c) between individual subscriber units 102(a)-(d) served by BS 100(a) and/or 102(b). More particularly, the designated geographical area of subscribers served by each BS 100(a) and 100(b) is typically called a cell 150, defined by its coverage area as shown in FIG. 2, where BS 100(a) and 100(b) are situated in designated cells 150(a) and 150(b). Within each cell 150(a) or 150(b) reside a plurality of subscribers 102(a)-(d) served by the BS 100(a) and/or 100(b) in the wireless internet access system. Typical cell coverage in urban areas is 2-3 kilometers, extending 4-5 kilometers in suburban or sparsely populated areas. Further, each BS 100(a) and (b) includes a plurality of access points (hereinafter xe2x80x9cAPxe2x80x9d, not shown in FIG. 1) serving as an interface between individual subscribers 102(a)-(d) of a cell 150(a)-(b) served by BS 100(a)-(b). Each access point includes receiver and transmitter circuitry of the base station for communicating with individual subscribers 102(a)-(d) within a designated cell 150(a)-(b).
Due to the need for increasing frequency spectrum reuse in the gigahertz band, in an effort to conserve this precious resource, the trend has been to reduce cell size even further (to microcells or picocells) which cover an even smaller geographical area, or which can serve hard to reach areas such as gullies and depressions where subscribers reside. Unfortunately this beneficial effect of increasing frequency spectrum reuse is offset by an increasing chance of neighboring cells interfering with each other, causing loss or degradation of the wireless signal. This loss or degradation of the wireless signal may be caused by, for example: (a) Rayleigh fading; (b) shadow fading due to obstructions from natural and man-made objects around the main transmission path of the subscriber""s devices; and (c) interference between co-channels and/or adjacent channels of wireless networks serving the subscriber""s devices.
Thus, in fixed wireless applications it is crucial to operation that the positioning of the wireless modem (WM) within a designated cell is properly aligned, so as to avoid or minimize the interfering effects of neighboring cells, or even possible effects from neighboring WMs within the same cell. To accomplish this, alignment of the WM is normally performed at initial installation.
For ease of installation and proper positioning of the WM within its designated cell or sector, a display device is provided on the side of the WM for diagnostics. This display device includes a plurality of LEDs that provide information to the installer, enabling him to verify that the WM is synchronized and communicating with the access point (AP) at the BS. Although the information provided by the display device is extremely helpful to the installer, it reflects the quality of communication in the forward link (commonly called downlink) direction only, which can be problematic.
For example, in a Rayleigh fading environment, the reflection and multi-path impairments of the reverse link (commonly called uplink) signal may be very different than that of the forward link signal. Although in the forward link direction a WM can establish a communication link with the AP with or without reflections from surfaces, this may be different from the reflection passed in the reverse link direction, WM to AP. If each signal on the opposite direction is bouncing off different surfaces, the delay spread in each direction and the signal strength may vary significantly from reverse link to forward link.
Therefore, there is a need to provide additional information, such as that reflecting the quality of communication in the reverse link direction, for example, on the same display device of the modem currently used for forward link indications. With both indications, an installer may adjust the communicating units to obtain an optimal position which accommodates proper signal quality for both reverse link and forward link directions.
The present invention provides a method and apparatus for aligning a first unit for wireless communications. A reverse link signal is transmitted from the first unit to a second unit, and the first unit is positioned based on at least one signal quality parameter of the reverse link signal which is contained in a forward link signal reply to the transmitted reverse link signal. More particularly, the method allows an installer to verify signal quality in both the forward link and reverse link directions on a display device of the first unit, repositioning the first unit until a received signal quality parameter for both paths exceeds a threshold value.